The present invention generally relates to printing apparatus and methods and more particularly relates to a printer and print head capable of printing in a plurality of dynamic ranges of ink droplet volumes, and method of assembling same.
An ink jet printer produces images on a receiver medium by ejecting ink droplets onto the receiver medium in an image-wise fashion. The advantages of non-impact, low-noise, low energy use, and low cost operation in addition to the capability of the printer to print on plain paper are largely responsible for the wide acceptance of ink jet printers in the marketplace.
Thus, ink jet printers are used in a variety of applications. For example, an ink jet printer may be required to print an image having a single density level at 180 dpi (dots per inch) for outdoor signage. This density level for outdoor signage is aesthetically acceptable because such images are typically viewed from a relatively long distance (e.g., 30 feet or 9.14 meters) away from the image. Ink jet printers are also called upon to print relatively high quality images having 16 density levels at 1440 dpi, such as in the case of 8 by 10 inch (20.32 by 25.4 centimeters) photographs. This density level for photographs is aesthetically desirable because photographs are typically viewed from a relatively short distance (e.g., 6 inches or 15.24 centimeters) away from the viewer.
However, available ink jet printers are not capable of printing both low density and high density ranges. The terminology "dynamic range" is commonly defined in the art to mean the range of minimum ink droplet volume to the maximum ink droplet volume which is provided by one ink nozzle. That is, each individual ink jet printer possesses a density range particularly suited for its intended use. For example, an ink jet printer used for signage typically has a density range different from the density range of an ink jet printer used for photographs. Clearly, for purposes of economy, it is desirable to have the same ink jet printer print in both low density and high density ranges.
Ink jet printers having continuous tone to high resolution printing performance are known. One such printer is disclosed in U.S. Pat. No. 5,412,410 titled "Ink Jet Printhead For continuous Tone And Text Printing" issued May 2, 1995, in the name of Ivan Rezanka. The Rezanka device provides a thermal ink jet print head both for continuous tone printing and high resolution printing by controlling the area covered by the ink at each pixel location of the printed image. The print head includes at least two different groups of differently sized nozzles from which ink droplets of different ink volumes are selectively ejected. Thus, according to the Rezanka patent, nozzles of one group, or both groups, may be selectively used to print continuous tone and/or high resolution text.
However, certain printing applications require a range of 16 to 256 different ink droplet volumes and it does not appear that the Rezanka device is capable of ejecting 16 to 256 different ink droplet volumes in a suitable manner. That is, it appears that the Rezanka device requires 16 to 256 nozzle groups to print 16 to 256 ink droplet volumes for a pixel in an image. Manufacturing such a great number of nozzles increases manufacturing and assembly costs of the printer and associated print head. Also, the Rezanka device appears to permit only a relatively small number of nozzles of a given nozzle diameter within each nozzle group. That is, it appears from the Rezanka disclosure that if a total of 256 nozzles having 256 nozzle sizes are present in a print head, there is only one nozzle for each nozzle diameter.
Moreover, it is known that the nozzle diameter may only be varied in a limited range to permit effective ink droplet ejection. In this regard, if the nozzle diameter is tool large, ink tends to inadvertently seep-out the nozzle. On the other hand, if the nozzle diameter is too small, viscosity forces acting at the nozzle wall will be too high for ink ejection. This limitation in variation of nozzle diameter further reduces the range of ink drop volumes that can be provided by prior art devices, such as the Rezanka device. Therefore, a problem in the art is limited range of ink drop volumes produced by ink jet printers.
Therefore, there has been a long-felt need to provide a printer and print head capable of printing in a plurality of dynamic ranges of ink droplet volumes, and method of assembling the printer and print head.